Copper Contact to Gold Surface Design Question

[gpalermo]

Hi,

I'm designing a "burn-in" station for a unique laser diode chip-on-carrier utilizing a 59 gold,99.99% electrical-grade), platinum, and tungsten contact pad for electrical conduction. The system is going to utilize soft, beryllium-copper 97.9% Cu - 2.1% Be leaf spring contacts to transmit the power upon contact.

This is the full setup of one rack with several carriers:



The full view is not really detailed enough, so here is a zoomed view showing the actual contact pads and spring on in place:



And just to get real detailed, I made a profile sketch showing the leaf spring contact unstressed in a bounding box. Please disregard the corner of the blade that is intersecting at the bottom right as that is being issued:





Soooo...

From this small background (which I hope is sufficient), I just wanted to know the following:

1) Is there a threshold force I can design the spring to exert upon the surface of the metalized contact pads to minimize, and if possible, eliminate surface defects?

2) Is there a way I can design the spring to fold easier upon the surface?

3) Are there any coatings or platings I can apply to the contact surfaces of the leaf spring that will allow an equally capable electrical power transmission between the two or give a surface finish that will eliminate scratching?


I'm under the impression that the Rockwell B Hardness of the CuBe leaf spring is 45-78 while the gold is so soft it can't be measured on the same scale. The only data I can find on the 59 gold is that it has a Vicker's hardness of 25-170, which is a huge range.... I do believe a Vicker's hardness of 150+ from the conversion chart I found here shows that the gold will be about as hard or harder than the copper-beryllium, which eliminates the worry altogether since a "harder" material cannot be scratched by the lesser one. Then again, that's just my knowledge from undergraduate materials classes so that could be a wrong assumption.

Oh, and nice forum!

My name is Graham and I work for a company called SemiNex which designs and manufactures high-power 1450 nm laser diodes.

[Gordon]

Hi Graham

to the Surface Engineering Forum.

Not sure what "59 gold" is but if it is relatively pure gold, then the hardness (~30 HV) will probably be much lower than the beryllium copper alloy. I would consider gold plating for the leaf springs primarily for good electrical contact and similar hardness. The leaf spring design I think should be optimised to give contact with minimum sliding motion between contact faces with the minimum force required to give the required electrical contact.

Hope that helps.

[Gordon]

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